1. Field of the Invention
This invention relates to a golf ball formed with a pair of half metal molds.
2. Description of the Related Art
A golf ball formed with a pair of half metal molds is made as that a wound string core or a solid core is covered with two semispherical shells and heated, or a cover is injection-molded to be spherical, and then, flash along a parting line, corresponding to a contact face of the metal molds, is cut and removed.
A golf ball is required to have similar flying characteristics when hitted in any direction, in other words, required to have no aerodynamic anisotropy. However, in the golf ball made as described above, dimple effect near the parting line is weakened for a problem that dimples can not be disposed on the parting line corresponding to a contact face of the metal mold, and another problem that dimples near the parting line are ground away when the flash on the parting line is cut, aerodynamic anisotropy becomes conspicuous, and difference is generated in flying ability of the ball by changing hitting point of the ball.
The difference of the flying ability is concretely as follows. When the golf ball is hit as that an axis L.sub.2 going through pole portions 3 is a rotational axis of back spin (this is occasionally called seam-hitting below) as shown in FIG. 6, trajectory of the ball tends to become lower and carry of the ball tends to become shorter in comparison with that of the other case in which the golf ball is hit as an axis L.sub.1 going through the parting line is a rotational axis of back spin (this is occasionally called pole-hitting below) as shown in FIG. 5.
Conventionally, a golf ball in which only dimples near a parting line are deeper than dimples disposed on the other parts of the ball to eliminate dispersion of trajectory and flying distance generated by difference of hitting point, is disclosed by U.S. Pat. No. 4,144,564, etc.
Although the trajectory in seam-hitting rises and comes close to the trajectory in pole-hitting by arranging only the dimples near the parting line to be deep as described above, the trajectory in seam-hitting is still lower than the trajectory in pole-hitting, the aerodynamic anisotropy of the ball can not be solved, and the dispersion of trajectory and flying distance is still generated.
It is therefore an object of the present invention to provide a golf ball with which the problems described above are solved, the aerodynamic anisotropy vanishes, and the flying ability becomes stable regardless of position of hitting point.